This invention relates to solar energy collection, and in particular to an arrangement for holding a number of rows of solar panels in a generally south-facing direction at an elevation angle that is chosen for optimal exposure to the sun. The invention is more particularly directed to improvements in a rack or frame arrangement including a series of pedestals or piers, a tubular support member supported on said piers in an east-west direction, and rail frame members that support the solar panels on either side of the axis defined by the tubular support member. The invention applies to solar collectors in which the panels are arrays of photovoltaic cells for generating electrical power, but the same principles can be applied also to arrangements for solar heating, for example.
Photovoltaic arrays are used for a variety of purposes, including use as a utility interactive power system, as a power supply for a remote or unmanned site, a cellular phone switch-site power supply, or a village power supply. These arrays can have a capacity from a few kilowatts to hundreds of kilowatts or more, and can be installed wherever there is a reasonably flat, unobstructed area with exposure to the sun for significant portions of the day. There are many such flat areas available, even in rather urban areas, and an abandoned athletic field is an example of such a location.
In general terms, solar tracker systems are often used, and these systems have their photovoltaic panels arrayed in rows supported on a torque tube that serves as an axis. In a solar tracking arrangement, a tracker drive system rotates or rocks the rows to keep the panels as square to the sun as possible. In solar trackers, the rows are arranged with their axes disposed in a north-south direction, and the trackers gradually rotate the rows of panels throughout the day from an east-facing direction in the morning to a west-facing direction in the afternoon. The rows of panels are brought back to the east-facing orientation for the next day.
However, in many cases, a fixed angle system may be employed, where the solar panels are positioned at a fixed elevation angle and at a fixed azimuth. These avoid the mechanical problems and expense of a solar tracker, and may be oriented to provide sufficient electrical power at peak demand periods, which are typically at about mid-day. In a latitude that corresponds to central United States, the solar panels would be faced generally to the south, and would be pitched at an angle approximately equal to the site latitude.
Wind loads and other weather phenomena require the support rack to be of sufficient strength to carry the load forces to the foundation in which the rack is mounted.
Conventional fixed angle solar collectors are often mounted on a prism-shaped support, like a rooftop, or may be mounted on a set of axial rails supported by at least two rows of vertical supports. These types of arrangement can be difficult to align, and may be costly to install because of the large number of supports that are needed for a given number of solar panels.
One fixed angle array of solar collector panels is described in Dalacu U.S. Pat. No. 6,201,179 in which a series of interlocking corrugated support members that may be anchored to a convenient rooftop. Another fixed angle array is described in Matlin et al. U.S. Pat. No. 4,966,631, in which each row of solar panels requires a front joist or horizontal support element and rear joist or horizontal support element, which are respectively supported atop a front row and a rear row of vertical support elements. The solar panels are then attached to rails that are carried transversely on the front and rear joists. This construction requires twice as many vertical supports as if a system were employed using single row of piers with an axial torsion bar supported atop the piers. In this system the electrical bus wires are carried in the open beneath the solar panels, and additional conduits have to be provided.
Accordingly, it is an object of the present invention to provide a fixed angle solar collector arrangement that avoids the drawbacks of the prior art.
It is another object to provide a fixed-angle solar collector arrangement that accommodates stresses and wind loading.
It is a further object to provide a solar collector arrangement that employs a single row of vertical support piers for each row of solar panels, thereby facilitating ease of installation.
It is a still further object to provide a fixed angle solar collector arrangement in which the fixed elevation angle can be set by means of a pier cap that is installed on each pier, which may be at a preset angle or may be field set.
In accordance with one aspect of the present invention, a solar energy collector arrangement has a support rack associated with each row of solar panels. An east-west oriented torsion tube defines an east-west axis for the row, with an array of flat rectangular solar panels attached along opposite sides of the torsion tube. There is at least one pier having a footing supported in a foundation, a member rising thereabove, and a pier cap affixed onto a top end of said pier member, and in which said torsion tube and its attached solar panels are held at a preset elevation angle. The torsion tube has an open (hollow) cross section, and is preferably formed of sections with swaged ends that can be connected in the field by inserting a swaged end of one section into an unswaged end of the next section. The hollow torsion tube may also be used as a conduit to carry the electrical conductors from the solar panels.
Preferably, the torsion tube has a polygonal cross section, i.e., square profile, rectangular profile, or other non-round profile. The pier caps have an aperture therethrough of a similar profile, and this is oriented to define the elevation angle for the torsion tube and the row of solar panels that it supports. The torsion tube is threaded through the pier caps, and then support rails are attached at right angles, i.e., radially, on the torsion tube. The solar panels are then fastened to the support rails.
The joints between the sections of the torsion tube may be welded to form a continuous rigid support. However, it is preferred that at least some of the joints left so that the swaged end be permitted at least a limited amount of slide in respect to the unswaged end of the next section so as to allow for thermal expansion. Likewise, the torsion tube may be welded to the pier caps where the tube passes through. However, at least some of these locations can also be left unwelded to allow for motion due to thermal expansion of the torsion tube.
The solar panel array can be installed employing a relatively straightforward procedure. First a rough staking is carried out over the entire field to confirm that all the elements of the array can fit on the site. The array is formed of a units which are considered Building Blocks, and in a practical embodiment the building blocks comprise sixty solar panels disposed on the torsion tube and supported on a set of four aligned piers. Each row can comprise one Building Block, or can comprise two, three, four, or more Building Blocks. There should be sufficient clearance between the ends of each row and the perimeter of the field.
Then a more detailed stakeout of the piers is conducted over the entire field. Preferably, permanent stakes are placed on the extended lines of the rows of piers, both on the east-west axis and on the north-south axis. Each pier location is then marked with a stake. Using a laser or level, the elevation is found for each pier location, to determine grade breaks and to determine the highest and lowest piers for each row. These data are used to ensure that there will be enough ground clearance, and to determine the desired cut-off elevation for the piers. All the piers should be cut so that their top ends are at the same elevation, i.e., so that the array will be level.
The piers are then installed, preferably installing the piers at the east and west ends of each row, plus one pier in each building block, or alternatively, in every other building block. Then, these piers are cut to their final elevation, and a taut string line can be used to establish line orientation for setting the remaining piers of each row. Witness stakes are set at each reference pier location, so that the pier locations can be quickly reset after pier holes are drilled.
Each pier is to be anchored in a concrete footing in the earth. For each pier, a pier hole is to be drilled, in which the pier is placed and held plumb while concrete is poured around it. If the pier hole will not stand open before the concrete is place, a temporary liner may be used. Only a limited number of pier holes should be drilled at a time, so that the holes being drilled and piers being installed at any one time can be protected and barricaded for the period of time until the concrete has been placed.
Each pier may be in the form of a tubular member, i.e., a pier tube, which is to be positioned in the pier hole and then plumbed and aligned at the proper location. The pier tube may be set in the hole bottom to stabilize the same during concrete placement. If the hole has been over-drilled, the pier tube may he held off bottom so that the top end of the pier tube reaches the final pier cut-off elevation.
The concrete mix that is employed should have a low slump. While the pier tubes are held in place in their plumbed location against the string line(s), the concrete may be placed, and vibrated into the hole around the tube. A fixture may be employed to hold the pier tube during concrete placement. The final pier location should be verified and adjustments made as necessary. The concrete top surface should be sloped for drain with a smooth troweled finish. The concrete is permitted to cure, and then the reference piers are cut off at the final pier elevation.
The remaining piers should be installed in similar fashion, and these also are cut off at the established final pier elevation.
The pier caps are then place loosely onto the tops of the pier tubes. These are cleaned of any corrosion, and may be given a coat of a zinc-rich galvanizing paint. Then, starting from the east end of each row the torsion tubes are threaded through the pier caps. The torsion tube sections are connected by inserting the unswaged end of the western torsion tube section onto the swaged end of the eastern torsion tube section. It may be necessary to drive these members together, e.g., with a mallet and plank. As the torsion tube sections are attached, the inside edge of each swaged end should be inspected for burrs and sharp edges, which should be filed smooth, if possible, as the torsion tube will be used as an electrical conduit. The torsion tube sections may be connected continuously for two successive Building Blocks (seven sections), but at the west end of each second Building Block the joint of the swage and unswaged ends should be left loose (unwelded) to allow for thermal expansion.
After the torsion tubes are all in position, the positions are checked to ensure that the piers do not interfere with module frame rail positions. Adjustments are made as needed between the torsion tubes and pier caps. Then the joints are welded, except, as mentioned above, for the joint between every other Building Block, which is left unwelded to accommodate thermal expansion of the torsion tube. Finally, the joints of the pier caps to the pier tube and to the torsion tube are welded, being careful to ensure that the torsion tube top surface is oriented at the appropriate fixed tilt angle, i.e., elevation angle. Thereafter, all the field welds are cleaned and coated with a zinc-rich cold galvanizing paint.
Using a template or fixture, the panel rails are located onto the torsion tube and are attached using hardware provided for that purpose. The panel rails are spaced at an interval that corresponds to the width dimension (i.e., east-west dimension) of the solar panels. The solar panels, i.e., photovoltaic modules, may be attached to the panel rails, with a side rail flange of one module overlapping a side rail flange of the next module in order that they can be mounted using the same threaded fastener, using care not to over-torque the module fasteners.
The hardware for holding the panel rails onto the torsion tube includes clamp members that have a central portion fitting over the torsion tube with a mating square profile and flange members at an open side of the central square portion that fasten to the associated panel rail. The rail members are supported at their middles on the torsion tube and are held against it by their associated clamps.
In a preferred mode, the pier cap weldments have a preset fixed angle, i.e., 30 degrees, 35 degrees, etc. However, in other embodiments, the pier caps can have an adjustable elevation angle to permit field adjustment upon installation. The pier cap can have a rotatable core, and can be held at the desired angle with a set screw or by welding at installation.
As an alternative, the pier caps can comprise a portion of the pier tube or pedestal, with a receptacle for the torsion tube being cut therein, e.g., by use of a coping fixture.
The above and many other objects, features, and advantages of this invention will become apparent from the ensuing description of a preferred embodiment, which is to be read in conjunction with the accompanying Drawing.